β ₂ -Microglobulin—A Free Immunoglobulin Domain

The SMALL SUBUNIT OF HL-A ANTIGENS IS SS2-Microglobulin

“…/32-microglobulin is a protein of tool wt 11,700 which is found in human urine and has already been sequenced (3)(4)(5). It is homologous in structure (both with regard to amino acid sequence and the position of an intrachain disulfide bridge) to the constant region domains of immunoglobulin polypeptide chains.…”

“…The antigen prepared by treatment of cells or cell membranes with papain contains polypeptide chains with a mol wt of about 34,000 and 11,000 (1), whereas the detergent-solubilized antigen has polypeptides of tool wt about 43,000 and 11,000 (2). Another membrane-bound protein found on human lymphocytes is ~2-microglobulin, an 11,700 mol wt polypeptide which was first isolated from the urine of patients with renal tubular disease (3) and which has subsequently been sequenced and shown to possess a moderate degree of sequence homology to constant region domains of immunoglobulin polypeptide chains (4,5).…”

Allelic variation in HLA-B and HLA-C sequences and the evolution of the HLA-B alleles

“…A characteristic feature of the classical class I products is their very high degree ofpolymorphism, mainly in the c~l and ~2 domain, which occurs within a highly organized framework of conserved sequences. The c~3 domain and B2m are relatively conserved and show amino acid sequence homology to immunoglobulin constant domains (Orr et al 1979, Peterson et al 1972, Trfigardh et al 1979, Smithies and Poulik 1972. The transmembrane and cytoplasmic regions contain the majority of locus-specific residues and reveal a higher degree of intralocus conservation which reflects evolutionary ancestry rather than positive selection (Gfissow et al 1987).…”

Crystallographic studies of bovine beta2-microglobulin.

“…Comparison of the amino acid sequence and other features of human #32-microglobulin with immunoglobulins (1,15) has indicated that it closely resembles the constant homology regions (16) of immunoglobulins G, M, and E. In intact immunoglobulin molecules, each homology region is closely associated with the corresponding homology region of another immunoglobulin chain in pairs of domains (16,17), whereas ,62-microglobulin is found associated with the heavy chain of HLA or H-2 antigens or the closely related thymus leukemia antigen (4-7, 18, 19), suggesting that such paired domains may be structural features of these cell surface molecules. In solution,…”

“…#2-Microglobulin is a protein distinguished by its similarity to certain portions of immunoglobulins (1)(2)(3) and by its association on cell surfaces with the major histocompatability antigens of man (HLA) and mouse (H-2) (4-7). Since its discovery in human urine in 1968, the overall properties, synthesis, and amino acid sequence of this protein have been characterized (2,(8)(9)(10)(11).…”